The hESC Core has been in existence since 2003, and has acquired and partially characterized 14 of the 21 NIH approved hESC lines. During this time it has established a reputation as an effective resource for hESC expertise within a highly collaborative scientific community. The Core will continue to assist PPG and UW/FHCRC investigators,characterize and store ESC lines, make the lines and derivatives available to investigators within the parameters of the MTA's, train investigators,devise new methods of hESC culture and characterize mico(mi)RNAsin undifferentiated and differentiated hESCs. In Specific Aim 1 we will support hESC research at UW/FHCRC by acquiring and characterizing the remaining seven NIH approved hESC lines, we will build an ES cell zoo,and we will continue to provide advice and assistance to UW/FHCRC investigators. In Specific Aim 2 we will develop second generation hESC culture conditions, building upon our initial observation that the 4 carbon fatty acid, butyrate,can support hESC self renewal in the absence of conditioned medium. We will also examine the effects of various matrices in the presence of butyrate. In Specific Aim 3 we will characterize all the NIH-Approved hESC lines for RNA and micro RNA Profiles, studies designed to reveal the function of microRNAs in hESCs.